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Full text of "Metallic zinc powder as a paint pigment / by H.A. Nelson, W.A. McKim."

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Metallic Zinc Powder 

as a 

Paint Pigment 

tew Jerseys 

Issued by 

The New Jersey Zinc Company 

(Established 1848) 

160 Front Street, j\ew York 


Metallic Zinc Powder 

as a 

Paint Pigment 

H. A. Nelson, M.A. 
W. A. McKim, M.S. 

tion, Resean li 1 1 
1 be Nen ferai ) Zin< < k>mpanj 



February io 26 

The New Jersey Zinc Company 

(Established 1848) 

L60 Front Street. New York 

Products Distributed l.v 

The New Jersey Zinc Sales Company 

\..v ^ ..rk Chicago Pittsburgh Cleveland San Francisco 

N : 

Z .: 

Metallic Zinc Powder as a Paint Pigment 

w ' " ' / '' I'owder is also known in the trade as Zinc Dust. 

aterial covered by this bulletin is no 1 a by-product made in 

zinc ores, but is distilled in furnaces especially 

designed and operated for the sole production of metallic zinc powder. 


' 3 r ' N,( IH SI was recommended and used in Europe as a paint pig- 
m menl mi leasl as earl} as I a 10. Reports h> recenl visitors in the 
*-^* industrial districts of France, Belgium and Western German} 
state thai zinc dusl paints are n..w used almosl exclusively for planl 
painting. Zinc dusl is also beiri tensivel} in marine paints, botli 

here and abroad. 

Practical tests, involving the application, to date, of about 2000 
gallons of paint, as well as the usual panel tests, have been made under 
the supervision of l his laboratory as follows: 

1. On steel and galvanized structures, both as the primer for the 
ordinary finish paints and as a final coat. These include sheet iron build- 
transformers, transmission towers, trestle work, tanks, efc 

2. On se< tions of the interior of a large industrial water lank. 

3. For repainting buildings on which the old paint was badl) cracked 
" mI which in rrial In ilrnml unless I he old paint was removed 
l>\ burning 

'• ^s a primer on sapp> redwood clapboards of a new house. 

5. For miscellaneous purposes, such as on screens, canvas roofs, 
interior ,,| ,, galvanized lighl exposure tank for accelerated weathering 

6. /mi dust has also been used as the pigment in lacquer enamels 
and as a tinting pigment stirred into outside white house [taints. 

These tests, plus the reports of tests in other laboratories, lead to the 

1. \s a nisi inhibitive metal primer it is at least equal to an> other 
high grade commercial primer. Ordinary finish coal paints adhere to it 
and give I h< m i rimum oi sei 

2. It also makes a gre} finish paint with a ver$ high hiding power 
thai completely covers an} surface in one coat. If hold, iu color and 
does not crack up >n i i 

3 Its peculiai property is that although the hard enough 

to shed dirt readily, the film maintains it- extensibility over long periods 
of time. This is perhaps due to an anti-oxident effect of the metallic zinc. 


This property makes zinc dust especially useful in repainting over old 
paint thai is badly cracked and must be firmly held in place. 

4. The same properties make it an excellent primer for refractor} 
woods, galvanized iron, sheet zinc and other surfaces that usually cause 
painting troubles due to poor adherence. 

5. The optimum amount of zinc oxide to use wit h zinc dusl forordmar} 
painting purposes is 10% to 25% by weight of the pigment. For priming 
iron and steel, about 20% zinc oxide is recommended. 

6. Ordinary Haw and Boiled Linseed Oil Vehicles give excellent 

7. It is eas} to prepare. Zinc dust needs onl\ be .stirred in dr\ with 
i with oil and zinc oxide paste. Zinc dusl incorporates equally well 

with lacquer enamel vehicles. 

8. With ordinary oil vehicles, zinc, dust does not 'take" hard in the 
om of (he container. Adding zinc oxide keeps it from settling. 

». Hydrogen gas is shnvly generated by the reaction between the 
divided metallic zinc in the zinc dust and any free acid in the \ eh icle. 
Hence, onl\ oil of low acid n an be used as the vehicle if the mate- 

to be stored in sealed containers, and acid driers, particularly must 
'I be used. Zinc dust-zinc oxide pastes made with a minimum ol lo* 
linseed oil (about 6 7 are practically free from this difficult) 
lu - ' d paints made with zinc dust do not "skin" readil) and 

can be very conveniently stored in containers with air vents, so thai foi 
ical purposes the acidit) ol the vehicle used is not a vital matter. 

11. No gas formation has hem detected when zinc dust is mixed 
with typical Lacquer enamel vehicles. 

12. This paint costs considerably [< ss than red lead paint. 

Metallic Zinc Powder 
as a Paint Pigment 

By if. \. Nelson wi> W. \. \1« Kim 



A LTHOl (ill the tests being conducted l»> this laboratory on the use 
[\ of zinc dusl as a paint pigment an- nol complete and final, theresults 
X A so far obtained are so encouraging thai the) are worth publishing. 
Other tests in the United States, as well as the histon of the use of zinc 
dust paints abroad, seem to check the favorable findings here reported. 
However, il is only by varied experience in main different uses lhal lla- 
real place of an> pigmenl or paint is determined, and il is the primar> 
purpose of this bulletin to presenl practical information and formulas so 
that known and tried paints ma) be made up l>\ those interested and an\ 
further experiments mosl wisely inaugurated. 

Histoid of the I si: or Zinc Dust \s \ Pvfm Pigmeni 

According to evidence in the literature and reports of persons who 
have lately visited there, zinc dust has hern and is being used m i onsiderable 
quantities in Continental Europe ;i- a painl pigment. 

Hie earliest known reh'ivncrs to I In- iim* of zinc dusl paint are b\ 
R. Mallei 1 in 1810 and b} S< uwarz 2 in 1861. followed b> Liecke 3 in L867. 
Lodin 4 in describing the manufacture of zinc dust, mentions paint as the 
first outlet for (Ik- material, stating thai " In former times zinc dust served 
• ■nl\ for the preparation <>i •• gre) p. tint destined to protect iron againsl 
oxidation . . ." 

Zerr and Rubencamp 5 , German authors, in describing zinc dust paint, 
refer to ils 1:0,1! . .onin- power and its sueeessful use as a rust inhibitor, 
lis use on machinery, sheet iron roofs etc., is recommended. 

R \I 1 ll<- 1 British A v Science 1840, p. 211. 

& It* .1 1 w ■- "• 1 - I iht% -I., n. hi i ■ 

Lieck< W •-><• i I ihresbi richl I 

\ I odin \1. 1 Jlurgie du Zim 

Zen tnd Rul p H 1 trbenfabrikation neile 181, 1908. 


™ N ^ IEBSE1 /,n, COMPAQ 

;:£- - «a,t 

Zinc Dusl 

linseed ( >iJ I 000 Kilo 

025 Kilo 

St :;:r t-"^ 

''' "''"";" " il " 1 "- "- I fo. steel, ,i 

that the French N ...,„,. . ,;„■ ^ ^ 

I I I 

M ". ; 

Zinc Oxide 

f iirpentine 

21'. l 

Persoj wi rfo/a mw/Z/v obtained fig //■ / // 

'", while studying Industry in Continent* 

proven thai large industrial plant* b 

ancdustpainU tclusivel 3 I , , , unpl< M Grunei 

• P ' plant oftheSociefc Inonynu d< M 
s de Zinc de la Vleille-Montagne, to 
s> has stated thai in I ;„ ( - dusl painl k 

mci s Industria 

''' ' " ..i,i 

composed ol dust, on. 

in linseed oil, turpentine and dj 

,,f ,,,r same : Hritfa this paint. I I 

llie Sarre Valley, whi< I 
and steel mi - the Dih\ ngen H 

ioU m this section 



\ » ! kii ent 1\ ill. earliesl reference to the use of zinc du^t in anti-cor- 
rosive paint in Vmerica is thai l>\ Henr} Williams in his description of 
the development of the Norfolk ship-bottom paint, now known as \a\> 
Departmenl formula No. 1 1. 

The next American reference to the superiority of zinc dusl as a metal 
protective paint was made in 1913 by D. Davidson". Test plates exposed 
outdoors two years and under water one yeai showed zinc dusl was in the 
besl condition of any at the end of the test. 

\> I' - l''l«> ( lardnei referred to the use of zinc dusl in paints 

for subaqueous exposure and recommended the wider use of this pigment 

for under-water paints. He u ajjain refers to zinc dust in L919, describing 

ellent results obtained after two-year outdoor exposure on metal panels. 

In regard to aging properties, Gardner 14 states that a paint composed 
of i'.n w. i_hi zinc dust and 2() ( \ raw linseed oil settled afire standing 
in containers for nine months. No caking was observed. This paint, 
after Wl months' exposure on metal panels, was described as hein^i in 

Uent condition, with onl} a slight amount of rust formed at the edges 
of the panel. This same paint when used as a primer with a finish coat of 
aluminum paint gave excellent results after 52 months" exposure. 

Following an entirely different line of endeavor Gardner 16 found that 
a paint made of equal parts by weight of zinc du^t and zinc oxide in a 
vehicle consisting of boiled linseed, turps and drier, when used as a primer 
on redwood and red cedar, effectively prevented resins from exuding from 
the wood and staining subsequent coats of white paint. This same paint 
when used as a primer on species of wood considered refractory to [taint. 
such ;t- i \ press reduced the tendency of the finish paint towards checking 
and cracking. 

\.-t\ recenl reports by Figg 17 before the Oil and Colour Chemists 
Association, of tests on water-line paints on the piers at Woolwich (Eng- 
land), are to the effect that after 58 weeks the results " indicate 
that for the conditions given, the best protection is afforded to steel work 
b\ two coats of a special paint consisting of zinc oxide and zinc dust in 
raw linseed oil." 

10 Hrtiry Willi. irn- Naval Constructor, 1 S Nav> Engineering Wewt \<>l 66 No " p. I.S7 August, 

11 D. Davidson, Metallic Pigments, Jour. Ind I Chem \..l ', t , 83 Jan I'H.'J. 
>« H. A. Gardner I 19 P VI \ M i . L916. 

II \ i. u-dnei I ir< ul tr No 61 P \1 \ V ( .ril. 1919. 

II \ *, miner. Cirrul .. \1 \ July. 1920. 

II \ Gardnei Circular No. 231, P. M. A., April, 1925 
« H. A. Gardner, Circular No. 222. \>. M. \ December 1924 
17 Chem. Trade Journal and Chem. Engineer, November 20, L925, p. 594. 



i I 
< ;, ' wo representative panels of a test s« ries -It. i ! 

£T!l!* ° H - SteeI I-"" i 

i the priming paints alone. 
I >ih- coal of the priming paints. 

* **■•" coat of the priming paints plus two industrial finish 


lwl N " ' Red l Paiie ] v , 2 /in , D 

IVmenl : >, Vehicle Vehicle 

i Red Lead <H\ H; )W Unseed Oil 75 /,,„ Dust Ran LinseedOil 

'/ ' 2.'', \\ Zin< OxidV I" rurpi 
3 J Oil |)ri«T OilD 


^< OPE OF Tl - l - 

Tin- i-\|m-i imenlal work conducted 1>\ this Laboratory on zinc dusl as 
a paint pigment includes outdoor exposures od standard tesl panels of 
steel and wood industrial slrurlure- ami hou rated 

weathering t<-i^- In this connection, to dale, over two thousand gallons 
of zinc dusl paint ha\e hern applied both l>> brush and spray method 
PalmertoD withoul encountering an\ difficulties in making l he change from 
other painl 

Some typical results of thes< tests are illustrated b> l lie photographs 
I hal are shown herewith. 

Figure I illustrates the present condition of two of a series of open 
hearth steel panels (12"x2l") thai have been exposed for V/± years a1 
a 15° angle, facing south, on a hillside overlooking an industrial plant. 
Panel No. 2 is painted with a 75% (by weight I zinc dust-25 ( , zinc oxide 
combination paint, as described in the figure, and Panel \o. I with 100* j 
red lead. Panel No. 2 is entirely on a par with Panel No. I. Moreover, the 
zinc dusl painl has the further advantage, proven by the color and general 
condition of section \ two coats of zinc dust-zinc oxide paint), thai it is 
entirely practical as a finish i oal as wt II as i u priming purposes. 

Figure II illustrates another sel of tests on ordinary Bessemer steel 
iMiiel>. Bessemer steel (copper content bekrw .05* , I panels are generally 
used in such exposure tests because of i heir tendency to corrode excessively 
!•> pitting, thus presenting the « ditions for a priming paint. For 

example, compare Figure I (a good grade (). II. Steel 
exposure with Figures II and III (Bessemer 3 ifter Pj to 2 y< 

, sposure. Copper bearing steels sho^w the same advantages of freedom 
from a pitting type of corrosion, and this is worth} of attention, in consid- 
ering plant maintenance by painting, no matter what paint is used. In 
Figure II the general superiority of Panel No 2 7.V , zinc dust-259< 
oxide is quite e> ident. 

Figure III illustrates another sel of tests on Bessemer steel exposed 
25 months under the same conditions. In this the paint on 

Pand V, 2 is 1 | zinc dust. The onl} corrosion on this panel is at the 

extreme lowei end of section "B" (1 coat zinc dust paint), whereas the 
characteristic pil I ing corrosion of Bessemer steel is more or less evident on 
the other two panels. 

Zinc dust-zinc oxide paints have been successfully applied l»> ordinary 
spray melhods to dozens of plant structures, such as illustrated in I i§ 
|\. II, iaph was taken one year after application of the paint, 


Mil M U II KM ^ /IM <«>\IP\M 






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Q -I & 5 


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onl\ one coat having been applied. The paint present- a i lean and uni- 
form appearance, as shown b\ Figun \ in spite oi the fad that this 
exposure is in a ver} dust} section of an industrial plant. 

Figure \1 illustrates the use of the spra\ irun in the application of 
a 7.7 j zinc dusl 25* J /in*' oxide paint on a highway bridge. The handling 
of zinc dusl [taints for spraying will be discussed in more detail later. 

\ year and a half ago, when the interior of an industrial vvalei lank 
was being painted, tesl strips of linseed oil paints made up with 7.7 , zinc 


FlGl i'. i l \ 

rypical job sprayed with zinc dust-zinc oxide painl 

Appearance is similar to thai of galvanized meta 

dust -")', zinc oxide were applied in two coats. Recently, th< n 
drained and the strips found to be in perfect condition, as showi 

ire VII. The superiority of the zinc dusl painl ovei the paint which 
has : l in painting such tanks w ' •' 

cleaner surfa< 2 both of which are evident the photograph. The paint previous!) used on th< 
tank- was an iroo oxide-zin tint, which had 

ius to i hi- repaint ii 



Probably the mosl striking illustration oi the exceptional adhering 
properties of zinc dust paints is shown by Figure VIII, which is a photo- 
s i aph of a section of the interior of the galvanized co\ er to 1 he accelerated 
weathering equipment in this laboratory. The question of getting paint 
to adhere tq the galvanized metal used in these tanks has always been a 
troublesome one. In this ease, the new galvanized iron cover was painted 
directl} with two coats of 75* , zinc dusl 25* , zinc oxide made up with 
boiled linseed oil) without ;m> previous roughening oi treatmenl of the 

Figi iu \ 

Close-up photograph of transformers showo in Figure l\ showing the clean 
sarance of the painl after one year of exposure in a dust} section ol an industrial 


surface. Althou-h the exposure to ultra-\iole1 lighl at LOO^ relative 
humidity and a temperature of 60°C. with periodic cooling has gone on 
uninterruptedly for over four months, the adherence to the galvanized sur- 
face remains perfect, rhere is absolutely no flaking a\\a\ of the paint 
film, when scraped with a knife. The severity of tie exposure is evident 
from the discoloration thai has occurred where accumulated moisture has 
dried on the surfa< e, 



Lax. i sheet zinc have painted with the same paint 

fie objectionable loose- 
be priming coat tha is s ind on surfaces of this 
kind repared for painting. It should be 

_ ri for safety, that sheet 
ith benzol, or treated 
iter to r- ible 









Ml- I \l.l H /l\( POWIHK \s v I'YIM PK.MEM 

in a plasti* material, where no shal lerin<r or I caring of the edges iN revealed 
even under the microscope, (b) Further shows how the paint could be 
pressed back into place and the cut practically healed b> molding the 
plastic paint. Obviously, this property of the zinc dust paint film makes it 
especially useful on repaint jobs, for example, where the condition of the 
old paint ma\ be sueh thai a brittle film must be avoided. Also, it un- 
doubtedly is this property that causes zinc dust paints to adhere so well to 
galvanized iron, sheet zinc and wood surfaces, on which it is difficult to 
obtain effective priming. 

This property i- further graphically demonstrated b> stress-strain 
measurements. -i nit ;e- shown in Figure V These tests were run h\ the 


'*v v v. V * SL : . W w 

1 A *} b 

Figure VII 

Interior of industrial water tank after 18 months' service. Photograph taken 
about 10 feet below water level. Note clean appearance and freedom from blisters 
on "B." 

-A"— Two coats of iron oxide-zinc oxide paint that has been successfully used for 
several years. 

"£" — Two coats. 

76 , Pigment : " 

TV, /„, h,M Haw O.t 

25% XX Zinc Oxide 4% Thinner 

/0 4% Gd Drier 



methods described in a Research Bulletin on "Some Physical Properties oi 
Painl and Varnish Films." The outstanding things indicated 1>\ such 
tests are I the relatively slight effecl on the physical properties oi tin 
film of changes in the relative humidity of the surrounding atmosphen 
2) the retention of distensive properties even after a relatively severe 
exposure to iiltra-violel lighl and (3) the superior general toughness oi 
I lie film, as indicated h> the longer stress-strain cm 

I J... RE \ ill 

Photograph of a section of the galvanized iron covei to an accelerated weathering 
equipment, tin- cover, painted without am weathering or copper sulfate treatmenl 
with ,.»', zinc dust J.V, zinc oxide paint, Ik.- been exposed to it.. 
light, l)« ;i i and moisture conditions in this tanl >ui months. Vdheren 

-till perfect. Paint QJm can no1 }„■ scraped clean from ili<- m 

I he attitude generally taken t>\ those writing about tl zin< 

dust as a paint pigment has been that it owt 
properties as a primer I ad steel I that zin< \s el ■ 

tive to iron and. hence, that zinc dust ofl 

K •■ 

LS.T. M \ 


are obtain.^ h> galvanizing. We have nothing to offer to shew that this 
may not be one point in favor of zinr .lust. bu1 the tough, plastic nature 
of the zinc dust paint film, just described, musl also be recognized as an 
important factor contributing to the excellenl protective and adhering 
qualities of the paint. 

Briefly considering the possible reasons lor this property of zinc dusl 
paint films, there are two major things thai can have determining effects 
on the distensibilit) of a paint film (in the absence of absorbed moisture 


i i i I \ 

Photomicrographs illustrating the plastic properties "I" ■■ /in< dust-zinc oxide 
l>;»inl film after exposure for one year on the smith -i<l( of .1 building. 

\ Showing typical cut in a plastic material. 

"B" — Paint film molded back into place and cul practically healed. Tit-- remain- 
ing in;irks were practically invisible to the naked eye 

which, in itself, has .1 softening effe< 1 . One is the retardation or arresting 
««f tin eontinnons oxidizing reaction thai normally takes place in the 
vehicle on | on » exposure. The other is the physical properties of the 
reaction products (soaps) formed in the film, which ma\ be soft and in 
themselves serve as plasticizers jusl as plasticizers function in lacquer 
enamels. The reaction products between zinc and f'alt> acids are do1 
known normally to possess such plastic properties, so it is more than 
probable that the action bere is mostly confined to retarding the continuous 
oxidation of the oil. One reaction product of a metallic zinc and the I'm 
acids, formed in the course of the oxidation of ilv oil, is hydrogen, which 
will be in a very reactive state. It is. then, easily conceivable thai this 
hydro-rri serves as an anti-oxidant (i.e., reacts with the oxygen in the 



lilm and thus retards the oxidation of the oil. The hydrogen formed is 
diffused through the film or used up in a reaction since no blistering takes 
place due to gas formation within the film. This theoretical phase of the 
subject is beinir investigated and will be reported on later. 

In spite of the plastic nature of the film and its very slight chalking 
tendencies, a zinc dust paint dries to a firm film on the surface and sheds 
dirt very well. This is especially true if from 15^ to 25 ( zun <>\; 
added. Their is no evidence of a tacky surface. 

Hiding Power 

Since it consists almost entirely of metallic zinc, zinc dust can not be 
appreciably transparent to ordinary visible light and, therefore, does not 

Age 3 DayslZ- Des/ccgrea ore ' 

P/g - /00% Ped I ead 
2S5/ZS of Pig per 6a 

P/a - 
f 125% UZ/nc t 

8 /is. of P/g per Gal of Potnf 

-s-t — +- 

/*0O0 &IOQC 32,000 4QOOC 

Load- Grems per - 

dust film. 


depend on diffraction of light by a large number of microscopic particles 
for its hiding power, as do the transparent pigments. It follows, of course, 
that any film that provides a perfectly continuous layer of zinc dust one or 
more zinc dust particles in thickness should completely hide the surface 
beneath. Cryptometer hiding power measurements on an 809c zinc 
dust-20% zinc oxide paint, taken over a white background, give readings 
of approximately 1800 square feet per gallon. (Ordinary outside white 
paints over black background will hide about 225 square feet per gallon.) 
One ordinary coat of a properly thinned zinc dust paint, even when con- 
siderable amounts of zinc oxide have been added, can be depended on to 
obscure cnl i rely a background of any color. 


Present Recommendations for the Prepar\tio\ wi> I se of Zinc 

Dust Paints 

1. Specifications for Zinc Dust 

We do not yet know the exact effect of variations in zinc dust on the 
quality of the paint films. The material that has been used throughout in 
exposure tests is a condensed zinc vapor, not atomized zinc. However, 
satisfactory paints have been prepared from atomized zinc dusts and there 
is no reason to doubt their efficacy in service. 

Fineness is an important factor. Generally, the somewhat grill > 
surface obtained with a moderately coarse zinc dust is not objectionable 
in a priming paint, because the rough surface furnishes such excellent 
anchorage for subsequent coats. But extreme coarseness encourages 
settling and causes trouble in spray guns. Early experiments were con- 
ducted with a zinc dust which met a specification of «><»' { t brought a screen 
of 45 micron opening (No. 325 screen). The film obtained vrith this mate- 
rial was quite gritty for a fmish surface, but not too much so for priming 
purposes. More recently a material meeting a specification of95' '< through 
a 45 micron opening (No. 325 screen) has been used very successfully. 
This has about sufficient coarse material for priming paints without showing 
any objectionable grit when used in a finish coat paint and can be recom- 
mended for general paint purposes. The following is a typical specification 
for material that has given entire satisfaction for all purposes: 

through 15-micron opening 
\ 125 screen) 
Fineness Iry » reening method 


Zinc Oxide 0—6.0 

|»1, 0—0 

o o 

Fe.'.'.'.'.Y.'.'.'.'. " " 



2 I se of Zinc Oxide With Zinc Dust 

The chief functions oi zin< oxide in zinc dusl paints are to harden the 
film to any desired extent and t< h<*lj> keep the zinc dust in suspension. 
According to our present knowledge, the latter is probably of more imme- 
diate importance. However, if coarse material is avoided, zinc dust itself 
shows surprising little tendency to settle am) does o< I cake. The addition 
of a small percentage oi zinc oxide practically eliminates all tendency to 
settle ( ired paint with -V, ziu< oxide have stood undis- 

turbed for n\ fi two years w i l Ik tut showing excessive settling or the ^liirhtest 
trace of caking at the bol torn. 

An\ zinc dust paint with up to 25 ( , zinc oxide cxhibils a -in i.i i-in_- 
amounl of the "tooth" that is so well liked b> painters in applying a paint 
with a brush. 

Still another function of zin< oxide is oi course, t«. brighten the color, 
the addition of 20^< > i- i r} pleasing medium grey, which is almosl 

an exacl match for The \cu Jers< Zin( I ompany's standard " Palmerton 
for plant painting. 

eriments have indicated throughout thai foi metal priming the 
amounl of zinc oxide used with zinc dusl should aot be ovei 25' ] and prei 
erabl} L5 to 20^ h\ weight) of the total pigmi 

■ ' niagi oi \ ehicle 

< >in ex] eriments have led t<» the conclusion thai a defia I in some "I 
ih»- zinc dusl paints used in the experiments described in the literature is the 
addition of too much vehicle. The vehicle content should !»«■ regulated 
to >i<*l(j a " .' -"I painting sive 1 binning .n - ided 

Willi an ordinary boiled linseed oil vehicle this will varj from appn 
match ,in 85 15 pigment-vehicli ratio Foi lOO^j zin< dusl to •■ 7U-22 
le ratio for 75^5 zincdu* - \\ zin< oxid< American 

I ' ■ ■ I I indi< ated undei i h( i m of i \ pica! formulae 

I d< pending on i he zin< dust and 

\ehid»- used. 

itile thinner is usual!) added («< ordinary paints to impi 

brusl be gloss oi und< rcoat Ul hough zin< dusl 

tial bi ushing pro| ertiee with* ut the addition oi 

volatile thinner, and the gritt) i Sim offers an i coellent an 

It feel i hat the inl rodu< il il« 

tbim _n' | 

MM VI IK /IM I'liUlilli \*. \ I'VINT PIGMEN1 

1. / , f Vi hicle to I 

Experiment- have indicated throughout that uniformly good exposure 
results can be expected from zinc dusl paints made with boiled oils or raw 
linseed oil and drier. Variations in the vehicles have not been studied to 
an} extent, although good results have also been obtained with certain 
treated oils of the semi-varnish type. 

The putting up of read} mixed paints containing zinc dust is com- 
plicated b> the slo^ reaction of the metallic zinc in the zinc dust with 
free acid in the vehicle to form hydrogen gas, which, if not released, may 
finally develop enough pressure to blow the cover off or open a seam. 
Hence, only pure linseed oil of low acidity (acid number below 4, prefer- 
ably) can be used if the mix is to be sealed away in containers for a period 
of time. The experimental work on the conditions governing the use of 
different vehicles and dryers in making ready mixed zinc dust [taints is not 
complete at this time. Apparently, the two most important precautions 
for retarding gas formation are L) to use only pure untreated moisture 
for oils of low acid number (below 6) and (2) to allow time for the free arid 
i" react, either with zinc oxide or the zinc dusl before the container is 
sealed. More detailed recommendations will be furnished as the experi- 
mental work progresses. Thro- is, however, a ver> practical way for so 
minimizing this tendency to generate gas that the mix can be handled lot 
shipping and storage, namely, to reduce the total oil contenl to the smallesl 
"""Mill that will yield a workable paste reads for thinning with linseed 
(, il and drier. The following is an example as a base for an HO' , zinc dust 
20* | zinc oxide paint: 

I (Mi |H>un<N W" Zinc Oxide (American Process Paste with IK' t 

•'528 pounds "Standard" Zinc Dust 
L 3 pounds Raw Linseed Oil of low acidity. 

The low total vehicle contenl <»| this paste 7' , offers a \<t> negligible 
possibilit> of a reaction and especially so if Iom acid moisture free oils 
;i '<" iiM-d in I \\r lii-| place. Such a pa-le set aside tor three months had not 
developed an} pressure in the can. Moreover, the paste has the further 
advantage that it is quite stiff and nerd not be sealed as tightly for trans- 
portation as would a more liquid paint. Neither pastes nor finished paints 
'"filaining zinc dust will -kin over readily and this adds to the ease of 
storing and handling them under working conditions, when containers are 
frequently lefl uncovered. For example, a paste made according to the 
above formula was set aside in an open quart can under a hot plate at a 
tem l erature about I5°C for eight days, and. at the end of this time, had 
shown abMi!ute|> no e\* of -i surfa< e skin. 



So special attention need be given to the acidity of the vehicle used 
where the paint is prepared on the job from zinc oxide paste and dry zinc 
dust or by thinning the zinc dust-zinc oxide paste, \lthou<m varnish 
vehicles max cause thickening. e\en quite hijdilx acid varnishes may be 
added it' (he paint is applied within about 21 hours at hi tiring mixed. 

.1. hn'rr to be I sed 

Zinc dust paints are normally moderately slow drying. One made 
with straight boiled oil and lhimi<-i rna> he loo slow drying lor some pur- 
poses requires about 30 hours to dn under moderate drxiny conditions . 
and then the addition of about 3* | l.\ weighl of the vehicle) of a standard 
lead-manganese oil drier is re< ommended. With raw linseed oil, the driei 
used should be a', to 6' h> weighl of vehicle . depending od drying 

For the reasons jusl stated (see pa^e 21) it is not practicable to use 
an} ordinary drier, which ma) be quite reactive, in a read) mixed zinc dust 
painl thai is to be stored in a sealed container. 

6. Preparation of the Painl 

Zinc dust pastes and paints should not !»«• ground in a paint mill. 
\n> properlx manufactured zin< dust is easily and thoroughly wetted 1>\ 
all oil and lacquer vehicles and ii i- onl) aecessar} to stir the pigment 
into iIh i vehicle h> the most convenient means at hand. No particular 
precautions arc uecessar> in adding zinc dust, for it will not "lump" as 
other metallic powders are likel) to do. In preparing the [tastes or paints 
weigh out the zinc oxide paste uot dr\ zinc oxide., thin gradually with 
part of the vehicle and stir in some zinc dust, adding oil and zinc dust 
alternately until th< ompleted. ( are should be taken thai the raw 

or boiled linseed oil which i^ used is pure and of high grade. 

7. Precautions in Handling Zinc I > 

l>r> zinc dust, in common with someothei metal powders, i- subject to 
bustion h\ oxidation if allowed to stand in contact with water. It 
should, ii be kept in a <U\ storage. ( ommercial shipments ar< 

in sealed tin containers and substantia] kegs that are moisture proof 

I plication 

Mo special manipulations are required in applying zinc dust paints 
b) the spra) method. \i the usual pressure foi industrial painting 60 to 
75 pounds pei squan inch the paint ma) even !»«• used as prepared foi 


brush application. Vi lower air pressures l"> h> ."> lbs. j >«i square inch 
i be painl musl be I binned. 

In general, the paints des< ribed belcra for brush application should b*' 
n-liiced with petroleum thinners (meeting I . S. Interdepartmental Speci- 
fications foi volatile thinners to a consistency that yields the besl results 
with the partit ulai apparatus .it band, and al skin drying under 

Qormal conditions "i mechanical application. However, the amounl of 
thinner added should qo1 exceed on< and one-half pints per gallon. 

I ndei normal conditions, when paint is to Ix- applied b> spraying, ih«* 
Qumbei of coats to be applied should be in a ratio of two coats b) spraying 

where thi il b} brushed method are called for. For two-coat spra} 

application, use the priming coat as specified foi regular three-coal work. 
Foi the finish the third coat painl specified for three-coat work, 

reduced to 3pra} ing consist* i 

On repaim work one coal uniformly applied l>> spraying is considered 
adequate aftei ui ■ bare spots have been properly primed with i In* specified 
priming painl. The finish coat shall be finish coat paint as specified for 
three-coal work, which is (binned for spraying, as mentioned above. 

( ). Typical Recommended Formulas 

When (be materia] must be sealed in closed containers for a more or 
less indefinite period <>f time, ii is reo tmmended that a zinc dust-zinc oxide- 
linseed oil paste be used according to the following specifications: 

Per ( Vni l,\ Weighl 
Maximum Minimum 

Pigment*... 94 

51 indard" Zinc Dus1 Kl 79 

\\ Zinc Oxide. 21 L9 

Vehicle 7 6 

Raw Linseed Oil \ \ belo* I 100 

This [K»Nir w«'i^b> atioul 17.2 pounds per gallon. 
From this paste, or an ordinary zinc-oxide-linseed paste, zinc dust 
(Mint t an be prepared as foil 

Piumi r Foi Metal Surfa< 

a I i in /ui' Dusl Zinc Oxide tinseed nil Paste 

/in. I lusl /in. < bade Paste 100 pounds 

R iu ..i Boiled Linseed < »il I ' i gallons 

I tinners ! z gallon 

Liquid Oil Drirr I ! _• pint- 

^i ield aboul ">' s gallons 

• I ii' pigment mixture should show on maryaifl not moi ' O and not leu 


ran m\\ iersei zinc company 

Zinc Oxide-Linseed Oil Pm 

" \.\ " / 

. . . 100 pou: 

With 18' 

•r Bofled Linseed Oil 

- . jIIS 


_ -ilons 

Liquid Oil DnVr 


: rod" Zin< Dust 

- pounds 

21". gallons 


'/ From Zin<- I I 

Zin< Du-t-Zir 

! ( >il 

_ lions 


: int ^ 

: iid Oil Drier 

> ield 

~> s 

From Zin* 

\\ / 


w. oa 

l Oil 


1 liinn^r^ 



; lid ( >il DnVr 

dard" Zir 


^ ield about 


Third < n\J Metal - 

I ' 

l < hi 



1 pint 

Liquid Oil Driers 

> ield about 

\ \ " Zi: 




1 ; 

/ Dust 


1". I 

da finis] \ 


\ \ " / 




11. Recapitulation of Some Special ( ses for Zinc Dust Paint 

For Prim am Galvanized Metal and Sheet Zinc: Zinc dusl paint has 
been found particularly useful on galvanized metal and sheel zinc where 
adherence depends on the retention by the oil in the film of its plastic and 
distensible properties. 

On Galvanized Fence: The present method of erecting galvanized fence 
and railing i^ such that often the zinc coating is cut from the iron. For 
example, this invariably occurs where pipe joints have to be rethreaded. 
The zinc dust-zinc oxide-linseed oil paste with about our [tint of liquid 
oil drier added to each 100 pounds of paste, add a littlr linseed oil also if 
the mix is too heavy), plastered on thr abraded places insures thorough 
protection a-ain-1 corrosion ,oid a\oids the marked color contrasts that 
natural!) result from t tie use of an> other realh high-grade rust-resisting 

For Priming Wood Surfaces: Zinc dusl paint makes an excellenl prime] 
for woods, such as cypress, red wood, etc., on which it is difficult to obtain 
good adherence. In this case, use the priming paint formula specified 
above, but add one pint of linseed oil and about one pint of benzol or some 
coal-tar thinner to each gallon of priming paint. The zinc dust paint 
affords good anchorage for any finish paint applied over it. 

On Canvas Roofs: Flat canvas roofs demand a paint that remains 
plastic. Zinc dust paint, with boiled linsrrd oil as the vehicle, has been 
found to be particularly suitable for such jobs, 

On Screens: Zinc dust paint (use finish coat pain I thinned slightly to 
prevent webbing) imparts a new galvanized appearance to screens and 
protects them from corrosion. One gallon will cover both sides of lift) 
ordinary house screens. 

Hot Surfaces: The mufller of an automobile, for example. usualK suf- 
fers from rust after several months' service, A coat of zinc dust paint has 
been found to prevent rust forming. The vehicle (ordinary linseed oil can 
be used) burns away, leaving a coating which preserves the metal. 

12. / se of Zinc Dust in Lacquer \ chicles 

Zinc dust isaseasilv welted by lacquer vehicles as it i> h> oil vehicles 
and no special mixing is necessary in preparing lacquer enamels with zinc 
dust. To obtain an exceptional!) smooth finish, the enamel should be 
allowed to age tor several days before applving. It makes an excellent 
tinting material which can be stirred in dry into an) finished lacquei 
enamel. \\ ith typical standard lacquer vehicles, no tendency to form gas 
in the containers has been observed. The addition of some zinc oxide is 
icrommeiidrd to retard settling. 



Zinc dust lacquers have been tested and can be recommended for 
metal, wood, stone and slate surfaces exposed both indoors and outdoors. 
\ typical formula for a light grey finish enamel for exterior use is as 
follows : 

Per Cent 

B> Weight 

Zinc- Dust 16.3% 

I rreen Seal Zinc Oxide :} I 

Y 2 Second R. S. Nitrocellulose SO Ucohol 16.9 

Castor Oil I ] 

Dil>ut\l Phthalate 5.9 

Damar 2 

Ester Gum 3.0 

Ethyl Vcetate ... IT o 

Butyl Acetate I I : 

\m>l Acetate. . . «) <> 

Butyl Alcohol. . 1.8 

Toluol 5.0 


To accommodate various spraying conditions the above formula may 
be extended to include further reduction with solvents and diluents. 

In order to obtain a satisfactory finish film a zinc dust of about 97% 
through l."i micron opening (No. 325 screen) is recommended, and coarse 
particles must be absent. For priming purposes, the fineness requirement 
are naturallx much less rigid. 

13. Use of Zinc Dust as a Tinting Pigment 

As a tinting pigment, zinc dust can be stirred in dry in any desired 
amount into ordinary outside paints. It has been so used with apparent 
beneficial effects on the physical proper i ies of the paint film. The resulting 
color is a clear blue grey, which can be readily modified by adding more . >r 
less dry zinc dust, or other tinting materials. 


New Jersey 


The World's Standard for Zinc Products